U.S. patent number 8,948,563 [Application Number 13/500,792] was granted by the patent office on 2015-02-03 for miniaturized on-line trace analysis.
This patent grant is currently assigned to Hochscule Regensburg, University of Applied Science. The grantee listed for this patent is Helmut Hummel, Alfred Lechner. Invention is credited to Helmut Hummel, Alfred Lechner.
United States Patent |
8,948,563 |
Hummel , et al. |
February 3, 2015 |
Miniaturized on-line trace analysis
Abstract
The invention relates to a measuring apparatus comprising an
apparatus for forming a liquid optical waveguide having a substrate
(1) having an at least partially curved closed microchannel (2)
having a low-refractive coating (13), whereby there is formed in
the substrate (1) at least one feed line (6) for supplying liquid,
and whereby there is provided at least at one end of the closed
microchannel (2) an apparatus for coupling light axially into the
closed microchannel and/or for coupling light axially out of the
closed microchannel (2), further comprising a light source (4), a
light detector (5), and a first liquid pump (9) which supplies a
sample liquid (7) to the closed microchannel (2) via the at least
one feed line (6, 6a).
Inventors: |
Hummel; Helmut (Schierling,
DE), Lechner; Alfred (Lappersdorf, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hummel; Helmut
Lechner; Alfred |
Schierling
Lappersdorf |
N/A
N/A |
DE
DE |
|
|
Assignee: |
Hochscule Regensburg, University of
Applied Science (Regensburg, DE)
|
Family
ID: |
43425896 |
Appl.
No.: |
13/500,792 |
Filed: |
October 5, 2010 |
PCT
Filed: |
October 05, 2010 |
PCT No.: |
PCT/EP2010/064833 |
371(c)(1),(2),(4) Date: |
June 27, 2012 |
PCT
Pub. No.: |
WO2011/042439 |
PCT
Pub. Date: |
April 14, 2011 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20120257193 A1 |
Oct 11, 2012 |
|
Foreign Application Priority Data
|
|
|
|
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Oct 6, 2009 [DE] |
|
|
10 2009 048 384 |
|
Current U.S.
Class: |
385/146 |
Current CPC
Class: |
B01F
13/0066 (20130101); B01L 3/502707 (20130101); G01N
21/645 (20130101); G01N 21/78 (20130101); G01N
21/31 (20130101); G01N 21/05 (20130101); Y10T
137/8376 (20150401); G01N 2021/6467 (20130101); G01N
2021/6482 (20130101); B01L 2300/0867 (20130101); G01N
2021/0378 (20130101); G01N 2021/056 (20130101); G01N
2021/0346 (20130101); G01N 2021/058 (20130101); G01N
2201/08 (20130101) |
Current International
Class: |
G02B
6/10 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1002005 028 166 |
|
Jun 2005 |
|
DE |
|
1 182 443 |
|
Feb 2002 |
|
EP |
|
99/57584 |
|
Nov 1999 |
|
WO |
|
WO99/57584 |
|
Nov 1999 |
|
WO |
|
Other References
Datta, Arindom et al., "Microfabrication and Characterization of
Teflon AF-Coated Liquid Core Waveguide Channels in Silicon", IEEE
Sensors Journal, vol. 3, No. 6, Dec. 2003, pp. 788-795. cited by
applicant .
Jiang, Linan et al., "Integrated waveguide with a microfluidic
channel in spiral geometry for spectroscopic applications", Applied
Physics Letters, vol. 90, Issue 11, Mar. 14, 2007, Abstract Only.
cited by applicant .
Hawkins, Aaron R., et al., "Optofluidic waveguides: II. Fabrication
and structures", NIH, Jul. 19, 2007, pp. 1/1-18/1. cited by
applicant .
Hawkins, Aaron R., et al., "Optofluidic waveguides: I. concepts and
implementations", NIH, Jan. 1, 2008, pp. 1/1-17/1. cited by
applicant .
Grosse, Axel et al., "Deep wet etching of fused silica glass for
hollow capillary optical leaky waveguides in microfluidic devices",
Journal of Micromechanics & Microengineering, vol. 11, No. 3,
May 1, 2001, pp. 257-262. cited by applicant .
Fouckhardt, H. et al., "Micro flow modules with combined fluid flow
channel and optical detection waveguide--hyper Rayleigh scattering
as a case study", Fresenius' Journal of Analytical Chemistry, vol.
371, No. 2, Sep. 1, 2001, pp. 218-227. cited by applicant .
Datta, Arindom, et al., "Microfabrication and characterization of
teflon af-coated liquid core waveguide channels in silicon", IEEE
Sensors Journal, vol. 3, No. 6, Dec. 1, 2003, pp. 788-795. cited by
applicant .
Jiang, Linen et al, "Integrated waveguide with a microfluidic
channel in spiral geometry for spectroscopic applications", Applied
Physics Letters, vol. 90, No. 11, Mar. 14, 2007, pp. 111108-111108.
cited by applicant .
Hawkins, Aaron R., et al., "Optofluidic waveguides: II. Fabrication
and structures", vol. 4, No. 1-2, Jul. 19, 2007, pp. 17-32. cited
by applicant.
|
Primary Examiner: Wong; Tina
Claims
The invention claimed is:
1. A measuring apparatus comprising: an apparatus for forming a
liquid optical waveguide comprising a silicon wafer as a substrate
(1) having an isotropically etched, spiral-shaped microchannel (2)
which is provided with a coating (13) that is low-refractive in
comparison with an aqueous solution, and which is covered with a
cover plate (12) for forming a closed microchannel (2), whereby the
cover plate (12) is provided with a further low-refractive coating
(13) at least above the microchannel (2), whereby there is formed
in the substrate (1) at least one feed line (6) which permits a
supplying of liquid into the closed microchannel (2) and/or a
removing of liquid from the closed microchannel (2), whereby a
respective feed line (6) is preferably formed at the ends of the
microchannel (2), and whereby there is provided at least at one end
of the closed microchannel (2), preferably at both ends of the
microchannel (2), an apparatus for coupling light axially into the
closed microchannel and/or for coupling light axially out of the
closed microchannel (2), as well as a light source (4) which is
adapted to penetrate the closed microchannel (2) with light, a
light detector (5), and a first liquid pump (9) which supplies a
sample liquid (7) to the closed microchannel (2) via the at least
one feed line (6, 6a).
2. The measuring apparatus according to claim 1, characterized in
that the measuring apparatus is adapted to provide a continuous
liquid stream within the microchannel.
3. The measuring apparatus according to claim 1 or 2, characterized
in that the apparatus for forming a liquid optical waveguide for
axially coupling light in and/or out is configured as a receiving
means for an optical waveguide (6) which permits a coupling in
and/or coupling out via the optical waveguide (6), whereby the
receiving means is preferably configured as an axial, straight
continuation of the microchannel within the substrate (1).
4. The measuring apparatus of claim 1, characterized in that the
cover plate (12) is light-transmissive, preferably consists of
quartz glass and is particularly preferably provided with a coating
(17) that is anti-reflective in the UV and VIS spectral ranges.
5. The measuring apparatus of claim 1, characterized in that a
micromixer (10) and/or a micropump (9) is formed in the at least
one feed line (6).
6. The measuring apparatus according to claim 5, further
comprising: a second liquid pump (9) which supplies a detection
liquid (8) to the closed microchannel (2) via a micromixer
(10).
7. The measuring apparatus according to any of claims 1, 2, 4, 5,
or 6, further comprising: a first optical waveguide (3) which is
adapted to couple light of the light source (4) axially into the
closed microchannel (2) at a first end of the closed microchannel
(2), whereby the light source (4) is preferably adapted to emit
monochromatic, visible light, and/or a second optical waveguide (3)
which is adapted to couple light axially out of the closed
microchannel (2) at a second end of the closed microchannel (2) and
to feed it to the light detector (11).
8. A measuring method for the measuring apparatus of claims 1, 2,
4, 5, or 6, the measuring method, comprising the steps of:
supplying sample liquid (7) and preferably detection liquid (8)
into the closed microchannel (2), transversally penetrating the
closed microchannel (2) with light of the light source (4), which
is preferably configured as an excitation light source, axially
coupling light out of the closed microchannel (2), detecting the
coupled-out light in the light detector (11).
9. A measuring method for the measuring apparatus of claims 1, 2,
4, 5, or 6, the measuring method, comprising the steps of:
supplying sample liquid (7) and preferably detection liquid (8)
into the closed microchannel (2), coupling light of the light
source (4) axially into the closed microchannel (2) at one end of
the closed microchannel (2), coupling transmitted light axially out
of the closed microchannel (2) at another end of the closed
microchannel (2), detecting the transmitted light in the light
detector (11).
10. The measuring method of claim 8, characterized in that a
continuous liquid stream is provided within the microchannel.
11. An apparatus for forming a liquid optical waveguide comprising
a silicon wafer as a substrate (1) having an isotropically etched,
spiral-shaped microchannel (2) which is provided with a coating
(13) that is low-refractive in comparison with an aqueous solution,
and which is covered with a cover plate (12) for forming a closed
microchannel (2), whereby the cover plate (12) is provided with a
further low-refractive coating (13) at least above the microchannel
(2).
12. The apparatus according to claim 11, characterized in that
there is formed in the substrate (1) at least one feed line (6)
which permits a supplying of liquid into the closed microchannel
(2) and/or a removing of liquid from the closed microchannel (2),
whereby a respective feed line (6) is preferably formed at the ends
of the microchannel (2).
13. The apparatus of claims 11 or 12, characterized in that at
least at one end of the closed microchannel (2), preferably at both
ends of the microchannel (2), there is provided an apparatus for
coupling light axially into the closed microchannel and/or for
coupling light axially out of the closed microchannel (2).
14. The apparatus according to claim 13, characterized in that the
apparatus for coupling light axially in and/or out is configured as
a receiving means for an optical waveguide (6), which permits a
coupling in and/or out via the optical waveguide (6), whereby the
receiving means is preferably configured as an axial, straight
continuation of the microchannel within the substrate (1).
15. The apparatus of claims 11 or 12, characterized in that the
cover plate (12) is light-transmissive, preferably consists of
quartz glass and is particularly preferably provided with a coating
(17) that is anti-reflective in the UV and VIS spectral ranges.
16. The apparatus of claim 12, characterized in that a micromixer
(10) and/or a micropump (9) is formed in the at least one feed line
(6).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from PCT/EP2010/064833, filed Oct.
5, 2010 and German Application No. 10 2009 048 384.5, filed Oct. 6,
2009.
This invention relates to an apparatus and a method for
spectroscopic measurement of substances dissolved in liquids. The
invention relates further to a method for manufacturing such an
apparatus.
In environmental analysis, in particular in water analysis, the
detection and measurement of substances dissolved in liquids in low
concentrations plays a great role. In this connection, different
spectroscopic methods such as absorption, transmission,
fluorescence and Raman are known. For this purpose, liquids are
analyzed for example in cuvettes or cells consisting of optically
transparent, light-conducting material, for example quartz glass.
To lower the detection limit of the substances to be detected, it
is known to realize light paths as long as possible within the
liquid in which the substance to be detected is dissolved. For this
purpose, there are used for example elongate cuvettes, capillaries
or also liquid optical waveguides in which the light losses
occurring along the long light path are reduced by a totally
reflective inside or outside coating. The refractive index of the
totally reflective coating here must be smaller than the refractive
index of the liquid, usually water, in the liquid optical
waveguide. Water possesses a refractive index of n=1.33. For
forming a liquid waveguide for aqueous solutions there can
therefore be used inside coatings of amorphous, fluorinated
polymers such as for example Teflon AF 1600 or Teflon AF 2400 with
refractive indices of 1.29 and 1.31 or also inorganic layer
materials, such as nanoporous silica films and silicon dioxides
with refractive indices as low as 1.18 or magnesium
fluoride-magnesium oxyhydroxide mixed layers with refractive
indices as low as 1.09. The stated refractive indices relate to the
wavelength of the sodium D line.
For realizing the above-mentioned long light paths there are
typically used liquid optical waveguides with lengths in the range
of several meters. This leads to considerable dimensions of the
resulting detection apparatus, a consequence being that the
intended detection measurements can frequently only be carried out
in the laboratory, whereas a prompt detection of such trace
substances on site is desirable for example directly on a body of
water to be analyzed. The dimensions of known apparatuses, however,
prevent such an on-site use, or at least make it considerably more
difficult.
Alternative measuring methods not requiring long light paths, such
as for example atomic absorption spectroscopy (AAS), the employment
of an inductively coupled plasma mass spectrometer (ICPMS) and ion
chromatography likewise involve very large and cost-intensive
devices.
The object of the present invention is to state a miniaturized
measuring apparatus that nevertheless creates a long light path
within the liquid to be analyzed, a manufacturing method for such a
measuring apparatus as well as a corresponding measuring
method.
The invention is based on the finding that, contrary to hitherto
known configurations, a liquid optical waveguide need not possess a
circular cross section, where the cross section is the area of the
hollow space to be filled with liquid that results upon a section
perpendicular to the longitudinal direction of the liquid optical
waveguide. In other words, a light conduction also takes place when
the cross section of the liquid optical waveguide deviates from the
known circular shape. Based on this finding is the idea underlying
the present invention to provide the liquid optical waveguide, not
as a self-supporting element, but as a closed microchannel on a
suitable substrate. A self-supporting liquid optical waveguide for
the purposes of the present print is an elongate hollow body that
is coated on the inside for forming a liquid optical waveguide and
consists of a material that is sufficiently stable mechanically so
that no further elements for stabilization are necessary. Such a
self-supporting liquid optical waveguide only needs to be mounted
at individual, spaced points.
Accordingly, the measuring apparatus of the invention comprises an
apparatus for forming a liquid optical waveguide. The latter
comprises a substrate having an at least partially curved
microchannel. After corresponding lining with a low-refractive
coating, after provision of a suitable cover and after filling with
liquid, the microchannel forms the liquid optical waveguide.
Through the at least partially curved forming of the microchannel,
an accordingly curved liquid optical waveguide is realized on the
substrate. Thus, the length of the liquid optical waveguide is not
limited by the outer dimensions of the substrate, as is the case
with straight microchannels. Rather, the microchannel can be
provided for example with a multiplicity of loops or windings on
the substrate surface, making it possible to realize a long
microchannel, and thus an accordingly long liquid optical
waveguide, despite small dimensions of the substrate.
The microchannel is preferably of spiral-shaped configuration,
whereby the center of the spiral coincides at least substantially
with the center of the circular disk. Particularly preferably, it
is an Archimedean spiral, wherein the radius of the spiral arm,
that is, of the microchannel, is proportional to the azimuthal
angle. For the purposes of the present print, the term
"spiral-shaped" is understood to refer to a shape that has at least
one complete revolution around a center and whose radius around
this center changes monotonically, preferably proportionally to the
azimuthal angle. The preferred spiral-shaped configuration of the
microchannel has the advantage that a multiplicity of closely
neighboring windings can be provided on the substrate surface.
Preferably, neighboring windings have a mutual spacing between 800
and 1500 .mu.m, preferably 800, 900, 1000, 1200 or 1500 .mu.m.
Thus, a great percentage area of the substrate surface can be
provided for forming the microchannel, thereby making it possible
to realize a great length of the microchannel and an accordingly
long light path in the liquid optical waveguide to be created.
Moreover, the curvature of the microchannel, that is, the change of
the longitudinal direction along the longitudinal direction,
changes continuously and monotonically, preferably linearly,
thereby maximizing the radius of curvature at each point of the
microchannel, avoiding small radii of curvature and thus minimizing
the flow resistance for the liquid within the liquid optical
waveguide to be formed. The monotonic course of the curvature of
the microchannel and of the corresponding liquid optical waveguide
further has the decisive advantage that only a minimum number of
loss modes occurs upon the light conduction, thereby maximizing the
light conductivity of the liquid optical waveguide to be formed.
Preferably, the minimum radius of curvature of the optionally
spiral-shaped microchannel amounts to 20 mm, 10 mm or 5 mm.
The microchannel preferably has a depth in the range between 50 and
500 .mu.m, in particular 200, 250, 300, 400 or 500 .mu.m, whereby
each of the stated single values can represent a boundary of the
stated values range. With such dimensions of the microchannel, a
laminar liquid flow can be realized in good approximation in the
later liquid optical waveguide, meaning that turbulences in the
liquid that disturb the spectroscopic analysis are avoided.
Further, the microchannel has an altogether small total volume
despite a great channel length because of the small channel cross
section, so that the minimum amount of a sample liquid to be
analyzed is small. The channel lengths preferably amount to more
than 1, 2, 3, 5, 10, 15, 20, 25 or 30 meters.
The low-refractive coating of the apparatus for forming a liquid
optical waveguide according to the invention possesses a thickness
of 2 to 10 .mu.m, in particular 2, 3, 4, 5 or 10 .mu.m, whereby the
stated single values can represent boundaries of the stated values
range. Preferably, the coating consists of Teflon, nanoporous
silicon dioxide or a nanoporous double compound of magnesium
fluoride-magnesium oxyhydroxide.
In the apparatus for forming a liquid optical waveguide according
to the invention, there is formed in the substrate a feed line
which permits a supplying and removing of liquid into the closed
microchannel and out of the closed microchannel. Preferably there
is formed at each end of the microchannel a respective feed line,
one of which supplies the liquid to the closed microchannel and the
other of which removes the liquid from the closed microchannel.
Thus, the liquid in the liquid optical waveguide can be easily
replaced and in particular a continuous liquid stream can also be
provided during the spectroscopic measurement, by for example the
liquid being pumped through the microchannel during the
spectroscopic measurement, which can be realized by a liquid pump
that is in operation during the spectroscopic measurement. It is
advantageous here when a laminar flow is present within the liquid
optical waveguide and turbulences in the liquid that disturb the
spectroscopic analysis are avoided. This is obtained according to
the invention by the feed lines extending non-axially with respect
to the longitudinal directions of the microchannel and preferably
forming an angle between 10 and 90 degrees, preferably 10, 15, 20,
30, 45, 60 or 90 degrees, with the longitudinal direction of the
microchannel at the intersection point between feed line and
microchannel. The stated single values can be boundaries of the
stated values range.
Further, there is provided on the substrate at least one end of the
closed microchannel, preferably at both ends of the closed
microchannel, an apparatus for coupling light axially into the
closed microchannel and/or out of the closed microchannel.
Preferably, the apparatus for axially coupling in and out is
configured as a receiving means for an optical waveguide, whereby
the receiving means forms an axial, straight continuation of the
microchannel within the substrate. Through the semi-circular cross
section of the microchannel, such an optical waveguide, in
particular a single-mode optical waveguide, can be positioned
suitably in the microchannel, in particular when the diameter of
the optical waveguide is equal to the depth of the microchannel.
Particularly preferably, there is provided in the microchannel
between the closed microchannel provided as a liquid optical
waveguide and the optical waveguide an element that guarantees an
effective coupling of light in and/or out. This is preferably a
microlens, in particular a GRIN (gradient-index) lens.
Alternatively, the apparatus for axially coupling light into and/or
out of the closed microchannel can be configured as a deflecting
unit which deflects light from the direction of the cover plate
axially into the closed microchannel and/or light from the closed
microchannel in the direction of the cover plate. This permits a
coupling of light into and/or out of the closed microchannel even
without an optical waveguide. The cover plate here has suitable
gaps or is light-transmissive, which can be obtained for example by
a cover plate of quartz glass. The deflecting unit can be for
example a micromirror arranged in the substrate.
A light-transmissive, transparent cover plate, for example of
quartz glass, has the advantage that the closed microchannel can
thereby also be penetrated by radiation transversally. This is
advantageous for example for fluorescence measurements and Raman
measurements, as to be explained more closely below.
In a preferred embodiment of the apparatus for forming a liquid
optical waveguide, a micromixer and/or a micropump is formed on the
at least one liquid feed line of the substrate. This makes it
possible, on the one hand, to further miniaturize the apparatus and
also the resulting measuring apparatus. On the other hand, the
provision of a micromixer permits the feed of two different
liquids, thereby increasing the degree of freedom in designing the
measuring method.
The measuring apparatus of the invention comprises, in addition to
the described apparatus for forming a liquid optical waveguide, a
light source, a light detector as well as a first liquid pump which
supplies a sample liquid to the closed microchannel via the at
least one feed line. The closed microchannel filled with the sample
liquid forms a liquid optical waveguide. In the sample liquid the
substance to be spectroscopically detected is present in dissolved
form. The sample liquid is preferably an aqueous solution, that is,
the refractive index of the sample liquid corresponds substantially
to the refractive index of water. The light source here is adapted
to penetrate the closed microchannel with light.
In a first embodiment of the measuring apparatus of the invention,
the latter is adapted for carrying out transmission measurements or
absorption measurements. For this purpose, the light of the light
source is coupled axially into the closed microchannel or the
liquid optical waveguide. This can be done via an optical
waveguide. In this case, the cover plate can be
light-non-transmissive and for example likewise be a silicon wafer.
Alternatively, the axial coupling in of the light of the light
source can also be realized by the above-described deflecting unit,
whereby in this case the cover plate has suitable gaps and/or is
light-transmissive. In basically analogous fashion, the transmitted
light is supplied to the light detector at the other end of the
microchannel, whereby this can again be done using an optical
waveguide or a suitable deflecting unit.
Depending on the chosen measuring method, the light of the light
source is monochromatic or broad-band and lies in the UV and/or
visible (VIS) wavelength range. Likewise, the transmitted light can
be supplied completely to the light detector, or it can be
spectrally filtered or split, for example via wavelength filters or
a spectrometric unit. Upon broad-band irradiation of light and
subsequent spectral splitting of the transmitted light, the latter
can be supplied to different light detectors, so that several
measurements can be carried out in parallel at different
wavelengths at the same time and thus different dissolved
substances can be measured at the same time.
In a particularly preferred embodiment, the light source emits
monochromatic light in the visible wavelength range, and the light
detector detects the total transmitted light without previous
spectral filtering. In a further preferred embodiment, the coupling
in and out is effected via the above-mentioned deflecting units, so
that the light source and the light detector can be arranged
directly on the substrate or the cover plate of the apparatus for
forming a liquid optical waveguide. For such an embodiment it is
particularly suitable to use LED diodes or semiconductor laser
diodes as a light source and photodiodes, for example avalanche
photodiodes, as a light detector, which are available as components
with small outer dimensions. This further miniaturizes the
measuring apparatus of the invention. Avalanche photodiodes are
highly sensitive and fast photodiodes that utilize the avalanche
effect, which is also employed in Zener diodes.
In a further preferred embodiment, the cover plate of the apparatus
for forming a liquid optical waveguide is light-transmissive and
preferably formed of quartz glass and particularly preferably
provided with a coating that is anti-reflective for the irradiated
light, for example for UV light. Thus, light of the light source,
which is preferably an excitation light source, can be irradiated
through the cover plate transversally, that is, perpendicular to
the longitudinal direction of the microchannel, whereby light is
coupled into the liquid optical waveguide at high yield through the
total or Fresnell reflection on the coated channel walls. This
arrangement is suited for fluorescence measurements and Raman
measurements, whereby the fluorescence light produced in the sample
liquid is collected by the liquid optical waveguide and conducted
to the ends of the liquid optical waveguide. In this embodiment, UV
light is preferably irradiated and the fluorescence light coupled
out axially and supplied to the light detector after optional
spectral filtering. In so doing, one can dispense with a spectral
filtering of the excitation light and thus a corresponding filter
element, because the transversally irradiated excitation light has
a great angle of incidence on the coating of the microchannel, so
that no total reflection takes place. Accordingly, the excitation
light is not conducted to the light detector through the liquid
optical waveguide.
The measuring apparatus of the invention and the measuring method
of the invention make it possible to detect many different
substances by characteristic absorption bands in transmission
measurements and absorption measurements. Depending on the
substance to be detected, the light of the light source as well as
a possible spectral filtering of the irradiated light are selected.
For example, there can be detected organic solvents such as
acetone, benzopyrene, benzene or anions such as nitrate or
phosphate which have characteristic absorption bands in the near UV
range. Likewise, there can be detected organic substances with a
conjugated .pi. system which typically have absorption bands in the
visible wavelength range. Likewise, Ni.sup.2+ has a characteristic
absorption band at 670 nm.
In the measuring apparatus of the invention, the liquid pump which
supplies the sample liquid to the closed microchannel is preferably
integrated as a micropump on the substrate of the apparatus for
forming a liquid optical waveguide. This makes it possible to
further miniaturize the measuring apparatus of the invention.
In a further preferred embodiment of the measuring apparatus, the
latter is configured to also supply to the closed microchannel a
second detection liquid besides the pump liquid. These two liquids
are mixed before being passed into the closed microchannel, which
is preferably done via a micromixer which is integrated in the
substrate of the apparatus for forming a liquid optical waveguide.
The detection liquid is supplied to the micromixer via a further
liquid pump, whereby the mix ratio of sample liquid and detection
liquid can be adjusted via the two liquid pumps. Preferably, both
liquid pumps are integrated as micropumps on the substrate of the
apparatus for forming a liquid optical waveguide, which further
miniaturizes the measuring apparatus of the invention.
In a particularly preferred embodiment of the measuring method of
the invention, metal ions are detected. A direct observation of
such metal ions by means of absorption measurement is generally
impossible, because metal ions typically have absorption bands in
the low UV range. In a preferred embodiment of the measuring method
of the invention, these metal ions trigger a detection reaction,
whereby the product of the detection reaction can be detected via
an absorption measurement. For this purpose, there is also supplied
to the closed microchannel, besides the sample liquid containing
the metal ions to be detected, a detection liquid in which a
suitable complexing agent is dissolved. Upon mixture of the sample
liquid and the detection liquid in the micromixer, the metal ions
enter into coordination compounds with the complexing agent,
whereby the resulting metal complexes have allowed charge-transfer
transitions with high extinction coefficients .epsilon. which
possess a strong absorption in the visible wavelength range. In
this case, the detection of metal ions can advantageously be
effected via the absorption of monochromatic visible light. A
further spectral filtering before the light detector is
advantageously unnecessary here.
In a first preferred embodiment of the measuring method, Cu.sup.2+
ions are detected and the complexing agent employed is
1,10-phenanthroline (C.sub.12H.sub.8N.sub.2). The resulting metal
complex possesses an absorption at 650 nm. In a further preferred
embodiment, Fe.sup.2+ ions are detected which form, with
1,10-phenanthroline as a complexing agent, a metal complex which
possesses an absorption at 510 nm. Likewise, Fe.sup.2+ ions can be
detected with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonic
acid)-1,2,4-triazine-5',5''-disodium salt
(C.sub.16H.sub.8N.sub.4Na.sub.2O.sub.8S.sub.2) as a complexing
agent, whereby the resulting complex shows an absorption at 567
nm.
A microchannel can in principle be provided in a substrate by
different methods, for example by embossing polymers, such as
polycarbonate, or milling. According to the invention, the
microchannel is incorporated into the substrate by etching,
preferably wet-chemical etching. For this purpose, a suitable
substrate is made available in a first step. Because the light
conduction within the liquid optical waveguide to be created
depends predominantly on the coating yet to be applied, so that the
substrate plays a minor role for the light conduction, a
multiplicity of substrates are in principle possible for the
apparatus of the invention. However, upon filling with the liquid
to be analyzed and possibly also during the measurement there occur
in the liquid optical waveguide high pressures which can be in the
order of magnitude of several bars. Hence, there is preferably made
available a substrate possessing an accordingly sufficient
mechanical stability. Materials to be used for the substrate are
therefore in particular quartz glass, borosilicate glasses such as
Pyrex glass, soda-lime glass, different polycarbonates and,
particularly preferably, silicon, for example a silicon wafer.
In a further step, there is applied to the substrate surface by for
example lithographic means an etching mask which defines the
microchannel to be formed. The material of the etching mask is
coordinated with the etching medium and the substrate. For etching
a silicon substrate in an acidic environment, for example, nitride
is a suitable material for the etching mask.
In a further step, the etching medium acts on the substrate at the
points specified by the etching mask. The etching medium is gaseous
or liquid and flows on the substrate surface to be etched at a
uniform flow velocity during the etching step. In other words, the
flow velocity remains constant in time at each point on the surface
of the substrate during the etching step, whereby different flow
velocities can occur at different points of the substrate. Thus, a
high reproducibility of the etched microchannel is attained.
Manufacturing the microchannel by etching according to the
invention has the advantage, in comparison to milled or embossed
microchannels, that it creates surfaces of high quality, that is,
smooth surfaces with low surface roughness, in the microchannel,
thereby improving the light conduction in the liquid optical
waveguide to be created.
Preferably, the etching in the substrate is isotropic, that is, the
etching velocity is substantially the same in all spatial
directions and independent for example of the crystallographic
planes in a silicon wafer. Thus, because of the uniform flow
velocity of the etching medium, there can advantageously be created
a microchannel with a substantially semi-circular cross section
whose depth is equal to or only slightly smaller than half of its
width. The depth of the microchannel here is the distance between
the plane of the substrate surface and the deepest point of the
microchannel on a sectional line extending perpendicular to the
longitudinal direction of the microchannel. The depth is measured
along the surface normal of the substrate surface. The width of the
microchannel is the distance between the intersection points of the
microchannel's inner walls with the substrate surface along a
sectional line extending perpendicular to the longitudinal
direction of the microchannel. The width is measured in the plane
of the substrate surface. The ratio between width and depth of the
etched microchannel, that is, the aspect ratio of the microchannel,
can be influenced in targeted fashion by the flow velocity of the
etching medium. Such a semi-circular microchannel is, on the one
hand, advantageous for the light conduction in the later liquid
optical waveguide and, on the other hand, permits the realization
of a simple axial coupling in and out of light by means of an
optical waveguide. The microchannel preferably has a depth in the
range between 50 and 500 .mu.m, in particular 200, 250, 300, 400 or
500 .mu.m, whereby each of the stated single values can represent a
boundary of the stated values range. With such dimensions of the
microchannel a laminar liquid flow can be realized in good
approximation in the later liquid optical waveguide, meaning that
turbulences in the liquid that disturb the spectroscopic analysis
are avoided. Further, the microchannel has an altogether small
total volume despite a great channel length because of the small
channel cross section, so that the minimum amount of a sample
liquid to be analyzed is small. The channel lengths preferably
amount to more than 1, 2, 3, 5, 10, 15, 20, 25 or 30 meters.
Preferably, the etching medium flows substantially in the direction
of the microchannel to be etched. This makes it possible to create
a microchannel with a semi-circular cross section, that is, a
microchannel whose width and depth are substantially identical.
If the substrate employed is a silicon single crystal, for example
a silicon wafer, the latter can in principle be etched with an
acidic as well as with an alkaline medium. Upon etching in an
alkaline environment, however, the crystal structure plays a great
role and the etch shape is defined by special crystal faces ({111}
etch stop areas). Thus, with an etching in an alkaline environment
an isotropic etching is impossible, as is a partially curved course
of the microchannel. In an acidic environment, however, the etching
is largely independent of the crystal structure. It is thus
possible to realize an isotropic etching which permits the forming
of an at least substantially semi-circular microchannel, and the
course of the at least partially curved microchannel on the
substrate surface can also be chosen at will, in particular
independently of the crystal structure of the silicon crystal.
In a preferred embodiment of the manufacturing method of the
invention, the substrate to be etched is of circular-disk-shaped
configuration, as is the case for example with a silicon wafer. If
during the etching step a stir bar conically tapered on both sides
or a discus-shaped stir disk is positioned centrally, above the
substrate surface to be etched, and rotated, this makes it possible
to realize in simple fashion a laminar, uniform and homogeneous
flow of the etching medium on the surface of the substrate to be
etched. The flow velocity is preferably radially homogeneous,
meaning that in at least a given radial region on the substrate
surface the etching medium flows in the azimuthal direction, so
that the flow velocity of the etching medium is identical at
different radii. In other words, in the given radial region the
rotational velocity of the etching medium is indirectly
proportional to the respective radius. In this connection,
"centrally" means that the axis of rotation and symmetry of the
stir bar or stir disk is a surface normal of the
circular-disk-shaped substrate and extends through the center of
the circular-disk-shaped substrate. Further, the microchannel to be
etched preferably extends on such a circular-disk-shaped substrate
substantially in the azimuthal direction with regard to the center
of the circular-disk-shaped substrate. Thus, there is produced with
the above-described stirring arrangement during the etching step a
laminar, uniform and radially homogeneous flow of the etching
medium, said flow going substantially in the direction of the
microchannel to be etched. The microchannel to be etched is
preferably of spiral-shaped configuration, whereby the center of
the spiral coincides at least substantially with the center of the
circular disk. Particularly preferably, it is an Archimedean
spiral, wherein the radius of the spiral arm, that is, of the
microchannel, is proportional to the azimuthal angle.
In a preferred embodiment of the microchannel manufacturing method
of the invention, the acting of the etching medium takes place in
several steps. Therebetween the etching is interrupted and the
substrate with the applied etching mask is rinsed with a suitable
substance, for example with water. Such a stepwise etching has the
advantage that the etching mask has higher stability during the
etching and thus a microchannel of high quality and depth can be
created. Preferably, there is employed for each etching step a
fresh, completely unspent, optionally newly prepared etching
medium.
After etching, the etching mask is removed. Before the microchannel
is closed, the inner wall of the microchannel can be smoothed by
being polished using gaseous hydrofluoric acid and gaseous
ozone.
Subsequently, the etched and optionally polished microchannel is
closed. For this purpose, in a first preferred embodiment of the
method, the etched microchannel is covered with a planar cover
plate. Subsequently, the cover plate is fastened to the substrate,
and the etched microchannel thereby closed, thereby forming a
closed microchannel. The materials of substrate and cover plate can
be identical or also be different. For example, a planar cover
plate of quartz glass can be fastened by anodic bonding to a
substrate of silicon, for example to a silicon wafer.
Alternatively, the cover plate can also itself consist of silicon
and be for example a further silicon wafer which is fastened to the
etched silicon wafer by means of silicon-silicon direct bonding
(SDB). Other materials and combinations of materials can also be
connected mechanically by bonding or other bonding processes.
Alternatively, all fastening methods are suitable that create a
sufficiently mechanically stable connection between substrate and
cover plate and at the same time create a sufficient liquid- and
light-tightness of the closed microchannel. In anodic bonding,
substrate and cover plate are brought to a high temperature, for
example 500.degree. C., and a high voltage, for example 1 kV, is
applied between substrate and cover plate.
In a further step, the closed channel is provided with a
low-refractive coating. Preferably, the coating consists of Teflon,
nanoporous silicon dioxide or a nanoporous double compound of
magnesium fluoride-magnesium oxyhydroxide. The coating material is
dissolved in a suitable solvent, for example FC40, FC75 or FC77,
and the solution injected into the closed microchannel. For this
purpose, there is introduced into the closed microchannel for
example a suitably formed cannula which suitably distributes within
the closed microchannel the solution with the coating material to
be applied. Subsequently, the closed microchannel is flushed with
gaseous nitrogen.
There is thereby created a closed, coated microchannel which is
hollow on the inside and forms a liquid optical waveguide when
filled with a suitable liquid having a higher refractive index than
the low-refractive coating, for example water. The closed
microchannel is completely lined with the low-refractive
coating.
In an alternative embodiment of the method for creating a closed,
coated microchannel, the substrate surface having the etched
microchannel and the surface of the planar cover plate are provided
with a low-refractive coating before substrate and cover plate are
joined. Preferably, the coating consists of Teflon, nanoporous
silicon dioxide or a nanoporous double compound of magnesium
fluoride-magnesium oxyhydroxide. For this purpose, a solution
having the coating material to be applied is applied to the
substrate surface having the etched microchannel and the surface of
the planar cover plate, for example by spin coating or spray
coating. Spin coating, also referred to as rotation coating, is a
method for applying thin and uniform layers or films to a
substrate. It is suited for applying basically any materials
present in solution. The substrate, for example a silicon wafer, is
fixed on a turntable and rotated at a certain speed and for a
certain time. A metering device above the center of the rotating
substrate is used to apply a desired amount of the solution,
whereby the solution is distributed uniformly over the substrate
surface and excess solution is spun off. Preferably, the solution
is applied in several steps and the substrate is heated between
these steps, so that the solvent evaporates and the optionally
nanoporous structure of the coating forms. In spray coating, there
is produced a fine mist of a solvent having coating material
dissolved therein, which is deposited on the substrate surface
having the etched microchannel and the surface of the planar cover
plate. After the evaporation of the solvent the coating material
previously dissolved in the solvent remains on the surface.
Preferably, the spray coating is also done in several steps, for
example in four steps, between which the substrate is rotated by
90.degree. and heated.
Subsequently, the substrate is covered with the planar cover plate,
so that the respective low-refractive coatings of the substrate
surface and the planar cover plate come to lie one on the other.
Subsequently, substrate and cover plate are stuck together by
heating substrate and cover plate. In so doing, the substrate and
cover plate, in particular when using Teflon as a coating material,
are heated above the glass temperature but not above the
destruction temperature of the coating material. Thus, the two
low-refractive coatings connect with each other, and there again
arises a closed microchannel that is completely lined with a
low-refractive coating.
Further embodiment examples and advantages of the invention will be
explained hereinafter by way of example with reference to the
accompanying figures. The examples represent preferred embodiments
which in no way limit the invention. The shown figures are
schematic representations that do not reflect the real proportions,
but serve to improve the clearness of the different embodiment
examples.
Specifically, the figures show:
FIG. 1 a schematic view of the measuring apparatus;
FIG. 2 a plan view of a spiral-shaped liquid optical waveguide;
FIG. 3 a cross section through a first embodiment example of a
coated, closed microchannel;
FIG. 4 a cross section through a second embodiment example of a
coated, closed microchannel;
FIG. 5 a longitudinal section through a measuring apparatus for
fluorescence measurement;
FIG. 6 an arrangement for etching a silicon substrate;
FIG. 7 a first embodiment example of a micromixer; and
FIG. 8 a second embodiment examples of a micromixer.
In FIG. 1 there is schematically represented an embodiment example
of a measuring apparatus. A spiral-shaped microchannel 2 is formed
here on a circular-disk-shaped silicon wafer 1. The microchannel is
coated with Teflon in the embodiment example and, upon supplying of
an aqueous solution, forms a liquid optical waveguide 2.
Alternatively, the microchannel can be coated with a nanoporous
silicon dioxide or magnesium fluoride-magnesium oxyhydroxide. The
microchannel 2 is covered with a cover plate not represented in
FIG. 1, so that there results a hermetically closed microchannel
which is light- and liquid-tight. The measuring apparatus further
comprises a monochromatic light source 4, a light detector 5 and
optical waveguides 3 which permit an axial coupling in and out of
light in the closed microchannel. Thus, on the one hand, the
monochromatic visible light of the light source 4 can be coupled
axially into the liquid optical waveguide and, on the other hand,
the transmitted light can be coupled axially out of the liquid
optical waveguide 2 and supplied to the light detector 5. This
allows absorption measurements and transmission measurements to be
performed in the liquid optical waveguide 2. As a light detector,
an avalanche diode is employed. Alternatively, other types of
photodiodes or other suitable light detectors can also be employed.
In particular, there can also be provided a spectral filtering (by
wavelength filter or by spectrometric methods) that precedes the
light detection. If the requirements for miniaturization are less
high, light sources and/or light detectors with greater dimensions
can also be employed, which are connected optically to the liquid
optical waveguide via for example self-supporting optical
waveguides 3. Between the liquid optical waveguide 2 and the
optical waveguides 3 there are provided microlenses (not
represented), for example GRIN (gradient-index) lenses, to increase
by their small aperture the yield of light coupled in and out.
Liquid is supplied to the liquid optical waveguide and removed via
feed lines 6, 6a, 6b. In so doing, a sample liquid 7 and a
detection liquid 8 are respectively pumped into the feed line 6 via
micropumps 9. Sample liquid 7 and detection liquid 8 are mixed in a
predetermined mix ratio in the micromixer 10 before being fed to
the liquid optical waveguide 2, whereby micromixer 10 and
micropumps 9 are represented separately from the silicon wafer 1 in
FIG. 1. In an alternative embodiment, however, the micropumps 9,
the micromixer 10 and the corresponding feed lines 6, 6a, 6b are
integrated on the silicon wafer 1, which leads to a considerable
miniaturization of the total measuring apparatus. In the measuring
apparatus the spectroscopic absorption measurements and
transmission measurements can be performed with the liquid still or
flowing within the liquid optical waveguide 2. The removed liquid
is collected in a collecting vessel 11 and can subsequently be
discarded.
In the measuring apparatus represented in FIG. 1 there is the
possibility of mixing two liquids in a predetermined mix ratio
before they are fed to the liquid optical waveguide. Thus, there
can be detected for example metal ions in the sample liquid 7.
These metal ions frequently have absorption bands in the low UV
range, which is not readily accessible to absorption measurements
and transmission measurements. An exception is for example the
Ni.sup.2+ ion, which in aqueous solution shows an absorption at 670
nm which can be employed for detecting such Ni.sup.2+ ions. The
sample liquid 7 having the metal ions dissolved in aqueous solution
is mixed with the detection liquid 8 in which a suitable complexing
agent is dissolved in likewise aqueous solution. The complexing
agent enters into a coordination compound with the metal ion,
whereby the resulting complex possesses allowed charge-transfer
transitions which possess a high extinction coefficient
(.epsilon.>1000) and lie in the visible spectral range. For
example, Cu.sup.2+ ions form with the complexing agent
1,10-phenanthroline (C.sub.12H.sub.8N.sub.2) an ionic complex
having one copper ion and three 1,10-phenanthroline molecules
([Cu(C.sub.12H.sub.8N.sub.2).sub.3].sup.2+), which possesses a
characteristic absorption band at 650 nm. With the same complexing
agent there can also be detected Fe.sup.2+ ions, which form with
1,10-phenanthroline an ionic complex of one Fe ion and three
1,10-phenanthroline molecules
([Fe(C.sub.12H.sub.8N.sub.2).sub.3].sup.2+), which possesses a
characteristic absorption band at 510 nm. Fe.sup.2+ ions can also
form with the anion of 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonic
acid)-1,2,4-triazine-5',5''-disodium salt
[C.sub.16H.sub.8N.sub.4O.sub.8S.sub.2].sup.2- a complex
[Fe(C.sub.16H.sub.8N.sub.4O.sub.8S.sub.2).sub.3].sup.4-), which
possesses a characteristic absorption at 567 nm.
The use of complexes for detecting metal ions has, on the one hand,
the advantage that the characteristic absorption of the formed
complex lies in the visible spectral range. This makes it possible
to employ as a light source light-emitting diodes (LEDs) or
semiconductor lasers, which are available as cost-efficient
components with small dimensions and can emit monochromatic light
in the visible wavelength range. The monochromatic light is
typically sufficiently narrow-band so that the total light can be
employed for the absorption measurement without previous spectral
filtering and be detected by a light detector without further
spectral filtering. Therefore, both as a light source and as a
light detector there can be employed components with small outer
dimensions which can advantageously be arranged directly on the
silicon wafer or a cover plate lying thereover. Thus, it is
possible, in sum, to integrate on the substrate a multiplicity of
the apparatuses necessary for feeding liquids and light, thereby
substantially miniaturizing the measuring apparatus.
The use of complexing agents for detecting metal ions has the
advantage that characteristic absorption bands in the visible
spectral range are created. Above all, their extinction is
considerably stronger than the extinction of the metal ions
themselves. Thus, the detection limit for metal ions can be
significantly lowered. The detection limit can also be considerably
lowered by the great channel length of the microchannel 2 and the
resulting long light path within the liquid optical waveguide 2.
Altogether, measurements in the sub-ppb range are thus
possible.
The embodiment example represented in FIG. 1 permits a miniaturized
construction of a measuring apparatus which nevertheless makes
great optical path lengths available and thus makes low detection
limits possible. The detection limit is lowered further by the
additional employment of suitable detection reactions.
In the embodiment example represented in FIG. 1 there is employed
as a substrate a four-inch silicon wafer in which a microchannel is
etched with a depth of 250 .mu.m. The microchannel is covered with
a light-transmissive, planar cover plate of quartz glass (not
represented). The microchannel is coated with a 3 .mu.m thick
coating of Teflon, so that the closed and coated microchannel 2
forms a liquid optical waveguide 2 for aqueous solutions.
In FIG. 2 the silicon wafer 1 is represented with a greater degree
of detail. The spiral-shaped microchannel 2, apart from the end
areas, is configured as an Archimedean spiral, that is, the radius
r of the microchannel 2 changes linearly with the azimuthal angle
.phi. of the spiral, starting from the center 18 (center of
symmetry) of the spiral. The spiral has a pitch of 600 .mu.m. The
pitch is the change of the radius r of the spiral-shaped
microchannel 2 after passing an azimuthal angle .phi. of 2.pi..
This guarantees a great total length of the microchannel and of the
corresponding liquid optical waveguide. In the shown embodiment
example, the length of the liquid optical waveguide amounts to
approx. 4.7 meters.
As to be seen in FIG. 2, the microchannel 2 is not continued to the
center 18 of the spiral, since light losses increasingly occur at
an increasing radius of curvature of such a liquid optical
waveguide, since the angle of incidence of light on the boundary
surface between the liquid core of the liquid optical waveguide and
the low-refractive coating becomes greater and thus the total
reflection condition is satisfied by a smaller proportion of the
light. In other words, the proportion of modes affected by light
loss in the liquid optical waveguide 2 increases. Hence, in the
embodiment example represented in FIG. 2, the spiral of the
microchannel 2 is guided on the four-inch silicon wafer disk only
up to a minimum spiral radius of 1 cm. Thereafter, the light is
coupled out of the liquid optical waveguide 2. Light losses on
account of the radius of curvature of the liquid optical waveguide
can be reduced by applying the low-refractive, totally reflective
coating in the microchannel 2 to a highly reflective substrate 1.
Such a highly reflective surface can be obtained employing silicon
as a substrate, because silicon is metallically reflective.
Further, it is advantageous in this connection when the
microchannel possesses a smooth surface, as is obtained for example
upon etching, in particular upon wet-chemical etching of such a
silicon substrate. Alternatively, the light losses can also be
reduced upon small radii of curvature when a totally reflective
coating with an especially small refractive index is employed. This
can be obtained by employing nanoporous silicon dioxide or
magnesium fluoride-magnesium oxyhydroxide.
As represented schematically in FIG. 2, light is axially coupled in
and out of the liquid optical waveguide for example via waveguides
3. Further, liquid is supplied to the liquid optical waveguide and
removed therefrom via feed lines 6. As to be seen in FIG. 2, the
feed lines 6 show an angle of 30.degree. relative to the
longitudinal axis of the microchannel 2. This ensures a laminar
flow within the liquid optical waveguide. Alternatively, other
angles between feed line and longitudinal axis of the liquid
optical waveguide can also be chosen in dependence on the chosen
hydraulic conditions within the liquid optical waveguide.
In FIGS. 3 and 4 there is represented a cross section through the
microchannel 2. In both figures the microchannel is hermetically
closed by a transparent cover plate 12 of for example quartz glass.
Further, the microchannel 2 is completely lined with a totally
reflective, low-refractive layer. The closed microchannel
represented in FIG. 3 was manufactured by fastening the quartz
glass cover plate 12 to the silicon substrate 1 by anodic bonding.
Subsequently, Teflon was injected into the closed microchannel and
flushed with gaseous nitrogen, so that the closed microchannel 2 is
enclosed completely by a totally reflective Teflon layer 13 having
a layer thickness of 3 .mu.m. By the anodic bonding there is
created a closed microchannel which is sufficiently liquid- and
light-tight to form a liquid optical waveguide.
The closed and coated microchannel represented in FIG. 4 was
manufactured by a manufacturing method alternative thereto. Here,
the quartz glass cover plate 12 and the etched silicon substrate 1
were first coated with Teflon by the spin coating method or spray
coating method. Subsequently, the substrate 1 and the cover plate
12 were placed with the coated sides one on the other and the total
arrangement was heated to a temperature of 330.degree. C.
Therefore, the Teflon coatings of substrate 1 and cover plate 12
stick together beside the etched microchannel 2 and there likewise
arises, in sum, a closed microchannel 2 which is completely
surrounded by a totally reflective layer 13 and is sufficiently
liquid- and light-tight to form a liquid optical waveguide.
In FIG. 5 there is represented a longitudinal section through a
measuring apparatus for fluorescence measurements. Here, excitation
light, for example UV light, is coupled into the liquid optical
waveguide 2 transversally through a quartz glass cover plate 12
(coming from above in the figure). In the liquid contained in the
liquid optical waveguide 2 there is produced fluorescence light
which is totally reflected on the low-refractive layer 13 and
conducted to the ends of the liquid optical waveguide 2. The cover
plate 12 is provided with a coating 17 that is anti-reflective in
the UV range, in order to minimize losses through reflection upon
the transversal coupling in of the excitation light. To increase
the yield of fluorescence light of the substance to be detected,
the substance can be labeled with fluorescent dyes beforehand and
subsequently measured. The represented measuring apparatus can
alternatively be employed for Raman measurements, where the
excitation light typically lies in the visible spectral range. The
anti-reflective coating 17 then acts anti-reflectively in the
visible spectral range.
In FIG. 6 there is schematically represented an embodiment example
of an apparatus setup for the etching of a silicon substrate 1.
Here, a circular-disk-shaped silicon wafer 1 with a diameter of
four inches is subjected to an etching solution 14. Etching takes
place in an acidic environment and the etching solution contains
acids such as hydrofluoric acid, acetic acid, nitric acid and/or
hydrogen peroxide in suitable proportions, optionally with
surfactant. In this liquid etching solution 14 the silicon wafer 1
to be etched is fastened in a suitable etching container with the
process side upward. The back side of the silicon wafer 1 located
below is passivated. The represented upward arrangement of the
process side of the silicon wafer 1 has the advantage that any
gases arising upon etching can escape easily. Two centimeters above
the circular-disk-shaped silicon wafer 1, a rotationally symmetric
stirrer 15 having a conical stir bar or a discus-shaped stir disk
19 is positioned centrally and rotated. This realizes a laminar
flow within the etching solution, resulting in a uniform,
homogeneous flow velocity of the etching medium on the wafer
surface. Such a laminar, homogeneous flow optimizes the etching
velocity, because spent etching solution is continuously removed at
every point of the wafer surface. The etching temperature here
should be within the diffusion-controlled region. Accordingly, the
etching velocities in the vertical direction, that is,
perpendicularly to the wafer surface, and the horizontal direction,
that is, along the wafer surface, are substantially equal, thereby
achieving in good approximation an isotropic etching and a
microchannel 2 with an accordingly semi-circular cross section.
Such a semi-circular cross section is represented schematically in
FIGS. 3 and 4. Further, the laminar, uniform flow on the process
surface of the silicon wafer guarantees a circular and smooth
etched trench and thus a microchannel 2 with a smooth surface and
low surface roughness.
For additionally smoothing the surface of the microchannel, the
microchannel can be treated, when required, with a gas mixture of
hydrofluoric acid and ozone. In so doing, the gas is distributed
over the total wafer uniformly via a nozzle array. This resulting
removal by polishing amounts to 1-2 .mu.m.
In the represented embodiment example, the etching of the
microchannel 2 is done in several steps. For example, each etching
step lasts four minutes. Subsequently, the silicon wafer 1 is
removed from the etching solution 14 and rinsed with water.
Subsequently, the silicon wafer is inserted into the etching
solution 14 again, a laminar flow of the etching solution 14
produced by means of the stirrer 15 again, and a further etching
step carried out with a predetermined duration and fresh, newly
prepared etching solution for example once more for four minutes.
Such a sequential etching in several etching steps, which are
interrupted by rinsing of the silicon wafer, improves the
durability of the etching mask, which consists of nitride in this
embodiment example. Thus, an uncontrolled widening is largely
avoided, and there is obtained a microchannel of high quality.
In FIG. 7 there is represented a micromixer which is integrated on
the silicon wafer 1. The micromixer 10 allows two liquids which
respectively flow via the feed lines 6a and 6b to be effectively
mixed and to be supplied to the liquid optical waveguide 2 via feed
lines 6. The feed lines 6a and 6b can be dimensioned in accordance
with the planned application, but are represented with an identical
diameter in FIG. 7. Because no turbulences are generally present in
microchannels, there would not occur any flow-induced mixture of
the two liquids (sample liquid 7 and detection liquid 8) upon
simple merging of the feed lines 6a and 6b into a common feed line
6.
In the micromixer represented in FIG. 7, the ends of the feed lines
6a and 6b form the input channels of the micromixer 10, and the
beginning of the feed line 6 the output channel of the micromixer
10. In FIG. 7, the input channels and the output channel are
arranged parallel. However, they can alternatively also be arranged
at an angle to each other. The two input channels and the output
channel are respectively connected via a multiplicity of parallel
flow channels 16 which are arranged at a non-right angle to the
input channels and the output channel. Neighboring flow channels 16
are respectively separated mutually by lamellae 20. The flow
channels have a length between 100 and 1000 .mu.m and a width
between 20 and 500 .mu.m.
The micromixer does not necessarily possess a symmetric
construction. It can rather be optimized to the planned application
and for this purpose be constructed differently on each side, that
is, in the part serving to feed the sample liquid 7 and in the part
serving to feed the detection liquid 8. In particular, different
lengths and/or different widths of the parallel flow channels can
be provided on each side.
In the embodiment example represented in FIG. 7, the lengths of the
flow channels are identical on each side and amount respectively to
1000 .mu.m. On the side represented on the left in FIG. 7, which
serves to feed the detection liquid 8 via the feed line 6b, the
flow channels have a width of 50 .mu.m. On the side represented on
the right in FIG. 7, which serves to feed the sample liquid 7 via
the feed line 6a, the flow channels 16 have a width of 500 .mu.m.
At the same width of the lamellae 20 separating the flow channels
16 of 100 .mu.m, the right side (sample liquid 7) of the micromixer
10, in the represented embodiment example, has in the region
between the input channel and the central output channel a lower
number of flow channels 16, an accordingly lower number of lamellae
20 and thus an altogether higher cross section of flow than the
corresponding left side (detection liquid 8) of the micromixer.
Thus, the micromixer 10 represented in FIG. 7 favors a mix ratio of
the resulting liquid mixture with a greater proportion of sample
liquid 7 and a smaller proportion of detection liquid 8. The mix
ratio is further influenced by the pumps provided in the feed lines
6a and 6b.
In the second embodiment example of the micromixer 10 represented
in FIG. 8, the two sides of the micromixer are constructed
identically. The length of the flow channels 16 amounts here to 200
.mu.m and the width of the flow channels 16 amounts to 50 .mu.m.
The width of the lamellae amounts to 20 .mu.m and the length of the
lamellae is equal to the length of the flow channels. Further, the
flow channels 16 are arranged mutually offset on the left and right
sides of the micromixer 10, so that the ends of the flow channels
16 respectively oppose the end face of a lamella. This construction
of the micromixer 10 produces in the output channel
small-dimensioned layer stacks of the two liquids to be mixed,
which mix quickly by diffusion. This effect also occurs in the
first embodiment example of the micromixer 10 represented in FIG.
7.
The micromixers represented in FIGS. 7 and 8 thus guarantee an
effective intermixing of two different liquids without employing
turbulences.
* * * * *